Doc: refine FAQ, add "What actions are required when a node restarts" #2707

Job	Run time
lint	6m 39s
cluster-benchmark (cluster_benchmark)	43s
external-stores (stores/rocksstore-v2)	9m 30s
openraft-feature-test (nightly)	1m 14s
openraft-feature-test (nightly, serde)	49s
openraft-test (stable, 0)	2m 58s
openraft-feature-test (nightly, single-term-leader)	47s
openraft-test-bench (nightly)	1m 44s
openraft-test (nightly, 30)	3m 12s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	49s
stores (memstore)	44s
openraft-test (nightly, 0, single-term-leader)	5m 4s
stores (rocksstore)	9m 49s
Build (nightly, bench,serde,bt,singlethreaded)	1m 13s
stores (rocksstore-compat07)	10m 46s
tests-feature-test (nightly)	2m 39s
stores (sledstore)	52s
tests-feature-test (nightly, single-term-leader)	2m 42s
examples (stable, raft-kv-memstore)	4m 15s
tests-feature-test (nightly, loosen-follower-log-revert)	4m 1s
examples (stable, raft-kv-rocksdb)	8m 6s
examples (nightly, raft-kv-memstore)	2m 8s
examples (nightly, raft-kv-rocksdb)	11m 41s
	1h 32m 25s

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